In Willing, U.S. Pat. No. 3,419,593, and in Karstedt, U.S. Pat. No. 3,775,452, are described complex catalysts comprised of platinum and unsaturated siloxanes, and their use in the so-called hydrosilation reaction between compounds containing silicon-bonded hydrogen and aliphatically unsaturated organic compounds, especially aliphatically unsaturated organopolysiloxane compounds. It is also known to use such catalysts in the reaction of organo silanol compounds with hydrogenosiloxanes to produce a new siloxane and hydrogen gas. Curable compositions useful as encapsulants for electronic components, and the like, comprise organopolysiloxanes having at least two aliphatically unsaturated groups or at least two silicon-bonded hydroxyl groups, a silicon hydride, and such platinum complex catalysts and these can be provided in foamable modifications, as well as filled modifications, containing e.g., from 10 to 300 parts of filler per 100 parts of organopolysiloxane. The disclosures of the above-mentioned patents are incorporated herein by reference, and the latter-mentioned ones as well.
The Willing patent describes, typically, the heating together of symmetrical divinyltetramethyldisiloxane in large excess with chloroplatinic acid then cooling, diluting with still more of the disiloxane, filtering and then washing with water to remove acidity. Adding trace amounts of this composition to a mixture of a polyhydrogenmethyl siloxane and a vinyl-terminated polydimethylsiloxane, followed by gentle heating produces a gel, indicating that the known reaction between the .tbd.Si and CH.sub.2 .dbd.CH- linkages has taken place.
Karstedt discloses that superior catalysts can be formed if pains are taken to remove all, or substantially all, of the inorganic halogen which is produced in the reaction between a platinum halide and an unsaturated siloxane. The use of a compound like sodium bicarbonate is specified to remove inorganic halogen before the platinum-siloxane complex is used as a catalyst.
In the present state of the art, catalysts prepared by the Willing method have been found to be somewhat less than satisfactory in terms of rate of cure, for example, due to the presence of detectable amounts of inorganic halides, and catalysts prepared by both the Willing and the Karstedt method are less than optimum because they contain numerous intermediate structures and they appear to be encumbered by inhibitory impurities. While both patents appear to recognize the need to remove undesirable materials, such as starting reactants, reaction by-products, etc., neither contemplates the presence, much less the need to avoid anticatalysts, i.e., the inhibitory impurities. See, for example, inhibitors as described in Nielsen, U.S. Pat. No. 3,383,356.
It has now been found that two types of olefinic siloxanes of a very specific nature can be used alone, or in combination, as complexes with platinum to produce superior catalysts, e.g., in the hydrosilation reactions of hydrogenosiloxanes with olefinically unsaturated and/or hydroxylated organic compounds and the hydrosilation reactions of hydrogensiloxanes with olefinically unsaturated and/or hydroxyl-substituted organosiloxanes. The olefinic siloxanes each are disiloxanes, one having one vinyldiorganosilyl group and one hydroxyldiorganosilyl group; and the second having two vinyldiorganosilyl end groups. It is essential that the complexes (i) be free of detectable inorganic halogen and (ii) be free of inhibitory impurities. These requirements can be met in either of two ways: (i) prepare the complex catalyst from a non-halogen-containing intermediate, e.g., the platinum bis-1,5-cyclooctadiene complex of Green et al., J. Chem. Soc., Chem-Comm. 1975, p. 3 and the respective disiloxane; or (ii) follow the procedure of the above-mentioned patents and isolate the complex catalyst free of halogen and inhibitory impurities by new techniques, such as preparative high pressure liquid chromatography. As will be seen hereinafter, the resulting complexes produce high cure rates and activity at low levels of platinum which are unattainable by following the teachings of the prior art.